1. Field of the Invention
The present invention relates to a varifocal lens barrel and a lens drive mechanism which can be used for the varifocal lens barrel.
2. Description of the Related Art
In an optical device, such as a photographing lens, a construction is known wherein in order to move lens groups thereof in the optical axis direction to perform focusing, etc., a set of cam tracks are formed on one of a pair of relatively rotatable ring members, and a set of followers are formed on the other of the pair of relatively rotatable ring members. The two ring members move relative to each other in the optical axis direction while rotating about the optical axis relative to each other via engagement of the cam tracks with the followers. There are cam track constructions known in the art such as a construction having cam grooves and followers respectively engaged in the cam grooves, and a construction having elongated protrusions having cam faces and followers respectively engaged with the cam faces. If such a construction is used in an optical device such as a photographing lens, play between the cam grooves or faces and the followers becomes a cause of tilt, eccentricity and/or axial positional deviation of a lens group or lens groups. Accordingly, it is desirable to reduce such play as much as possible while ensuring a smooth movement of each follower pin relative to the associated cam groove or cam face to achieve a stable image performance. Each follower preferably slides on the associated cam groove or cam face as smoothly as possible to ensure proper and precise movement of a lens group or lens groups.
A varifocal lens which requires slight focus adjustment when zooming, unless focused on infinity, is known in the art. In a varifocal lens, an axial position of the focusing lens group to focus on an object at a fixed distance slightly varies if the focal length is changed. In a varifocal lens of an AF (autofocus) lens-shutter camera, an axial position of the focusing lens group from the standby position thereof to focus on the object only needs to be determined so as to compensate for such a slight focus variation. On the other hand, in a varifocal lens of an MF (manual focus) SLR camera, such a slight focus variation can be adjusted by turning a focus ring while viewing an image of the object through the viewfinder; accordingly, in general use, such a slight focus variation is not a substantial obstacle to focusing operation itself.
However, a distance ring of a varifocal lens used for SLR cameras needs to be provided thereon with a distance scale for the photographer to read, so that an object at a distance indicated by the distance scale must be brought into focus at any set focal length. In other words, when focusing on an object at a fixed distance, the varifocal lens needs to bring the object into focus by moving the focusing lens group from the standby position thereof by different amounts of movement at different focal lengths, respectively, by turning the distance ring by the same amount of rotation from the infinite position thereof. Accordingly, in terms of a focal length varying operation, a varifocal lens used for SLR cameras is required to have a function to vary the focal length without disturbing focus, similar to that of a zoom lens. The structure of this type of varifocal lens is generally complicated; furthermore, it is difficult to eliminate interference between a focus cam, which is used for changing an amount of movement of the focusing lens group from the standby position thereof per unit of rotation angle of the distance ring in accordance with a variation of focal length, and a zoom cam for zooming operation. Even if interference between the focus cam and the zoom cam is eliminated, the image performance of the varifocal lens is sensitive to tilt, eccentricity and axial positional deviation of the focusing lens group. Therefore, it is desirable to reduce play in a support/guide mechanism for the focusing lens group as small as possible to stabilize the image performance of the varifocal lens and to move the focusing lens group as smooth as possible.
The present invention provides a varifocal lens barrel in which tilt, eccentricity and axial positional deviation of a focusing lens group is prevented from occurring while a smooth movement of the focusing lens group is ensured to thereby achieve a stable image performance.
The present invention also provides a lens drive mechanism having two rotating rings rotatable relative to each other in an optical device such as a photographing lens, wherein tilt, eccentricity and axial positional deviation of a movable lens group (e.g., a focusing lens group of a varifocal lens) are prevented from occurring while a smooth movement of the focusing lens group is ensured to thereby achieve a stable image performance.
For example, in an embodiment, a varifocal lens barrel is provided, including a varifocal optical system having a plurality of movable lens groups which are driven to move in the optical axis direction to vary a focal length, wherein the plurality of movable lens groups include a focusing lens group which is moved by different amounts of movement at different focal lengths, respectively, when focusing on an object at a fixed distance; a focus operation ring which is manually rotatable; a focus lens frame which supports the focusing lens group, the focus lens frame being rotated via rotation of the focus operation ring; a guide ring positioned around the focus lens frame; a bottomed focusing cam groove having a non-linear contour which is formed on one of an outer peripheral surface of the focus lens frame and an inner peripheral surface of the guide ring; a spherical follower which is supported by the other of the outer peripheral surface of the focus lens frame and the inner peripheral surface of the guide ring, the spherical follower being movable in a radial direction of the focus lens frame and the guide ring and slidably engaged in the bottomed focusing cam groove so as to move the focus lens frame in the optical axis direction in accordance with the non-linear contour when the focus lens frame is rotated by rotation of the focus operation ring; a biasing member for pressing the spherical follower against the bottomed focusing cam groove; and an adjustment mechanism which varies a relative moving range of the spherical follower in the bottomed focusing cam groove, in a circumferential direction of the guide ring, in accordance with a variation of the focal length to vary an amount of movement of the focusing lens group per unit of rotation of the focus operation ring in accordance with the focal length.
The varifocal lens barrel can further include a zoom operation ring which is manually rotatable independently of the focus operation ring; an intermediate movable frame which supports the focusing lens group via the guide ring, the intermediate movable frame being guided in the optical axis direction without rotating about the optical axis; and a zoom drive ring which moves the plurality of movable lens groups and the intermediate movable frame in the optical axis direction in a predetermined moving pattern via rotation of the zoom operation ring. The adjustment mechanism includes a rotation transfer member via which rotation of the zoom drive ring is transferred to the guide ring to rotate the zoom drive ring and the guide ring together about the optical axis while allowing the guide ring to move in the optical axis direction relative to the zoom drive ring; an adjustment cam portion having a non-linear contour which is formed on one of opposed peripheral surfaces of the intermediate movable frame and the guide ring, the non-linear contour of the adjustment cam portion being to the same as the non-linear contour of the bottomed focusing cam groove; and an adjustment follower formed on the other of the opposed peripheral surfaces of the intermediate movable frame and the guide ring to be engaged with the adjustment cam portion. The guide ring rotates about the optical axis while moving in the optical axis direction relative to each of the focus lens frame and the intermediate movable frame by same angle of rotations about the optical axis and by same amounts of movement in the optical axis direction to thereby vary the position of engagement of the spherical follower with respect to the bottomed cam groove when the adjustment follower and the spherical follower are positioned at a common circumferential position relative to the adjustment cam portion and the bottomed cam groove, respectively.
The varifocal lens barrel can further include a stationary barrel which supports the zoom drive ring so that the zoom drive ring moves in the optical axis direction when rotated about the optical axis relative to the stationary barrel. The zoom drive ring supports the intermediate movable frame so that the intermediate movable frame is rotatable about the optical axis relative to the zoom drive ring without moving in the optical axis direction relative to the zoom drive ring.
The bottomed focusing cam groove can be formed on an outer peripheral surface of the focus lens frame, and the spherical follower can be provided on an inner peripheral surface of the guide ring.
It is desirable for there to be three bottomed cam grooves arranged at equi-angular intervals in the circumferential direction, three spherical followers arranged to correspond to the three bottomed focusing cam grooves, and three biasing members arranged to correspond to the three spherical followers.
The bottomed focusing cam groove can be formed to have a trapezoidal cross section so that a width of the each the bottomed focusing cam groove increases in a radial outward direction.
The bottomed focusing cam groove can be formed to have a V-shaped cross section so that a width of the each the bottomed focusing cam groove increases in a radial outward direction.
The bottomed focusing cam groove can be formed to have a circular arc cross section so that a width of the each the bottomed focusing cam groove increases in a radial outward direction.
The biasing member can be a helical spring which is supported by one of the guide ring and the focus lens frame which supports the spherical follower.
The biasing member can be a cantilever leaf spring, wherein one end of the cantilever leaf spring is fixed to one of the guide ring and the focus lens frame which supports the spherical follower.
The biasing member can be a leaf spring, wherein opposite ends of the leaf spring are fixed to one of the guide ring and the focus lens frame which supports the spherical follower.
The one of the guide ring and the focus lens frame which supports the spherical follower can include a holding portion which holds the one end of the cantilever leaf spring.
The one of the guide ring and the focus lens frame which supports the spherical follower can include two holding portions which hold the opposite ends of the leaf spring, respectively.
The biasing member can be a leaf spring portion which is formed integral with the one of the guide ring and the focus lens frame which supports the at least one spherical follower.
The spherical follower can be made of metal or synthetic resin. The biasing member can be made of metal or synthetic resin.
The bottomed focusing cam groove can be formed integral with the one of the guide ring and the focus lens frame which supports the spherical follower, when the one of the guide ring and the focus lens frame which supports the spherical follower is molded of synthetic resin.
It is desirable for at least the bottomed focusing cam groove to be made of metal.
In another embodiment, a lens drive mechanism is provided which moves a movable lens frame supporting a movable lens group in the optical axis direction by a relative rotation between the movable lens frame and a guide ring which are coaxially arranged, the lens drive mechanism including a radial hole formed on one of the guide ring and the movable lens frame; a spherical follower inserted into the radial hole, the spherical follower being slidable in the radial hole; a guide groove formed on the other of the guide ring and the movable lens frame; and a biasing member which biases the spherical follower in a direction to come into pressing contact with the guide groove.
The guide groove can include an operating portion which has a non-linear contour.
Alternatively, the guide groove can include an operating portion which has a linear contour.
The lens drive mechanism can include three guide grooves arranged at regular intervals in a circumferential direction, three spherical followers arranged at regular intervals in a circumferential direction, and three biasing members arranged at regular intervals in a circumferential direction.
The guide groove can be formed so as to have a trapezoidal cross section, so that a width of the guide groove increases in a radial outward direction.
The guide groove can be formed so as to have a V-shaped cross section, so that a width of the guide groove increases in a radial outward direction.
The guide groove can be formed so as to have a circular arc cross section, so that a width of the guide groove increases in a radial outward direction.
The biasing member can be a helical spring which is supported by one of the guide ring and the movable lens frame which supports the spherical follower.
The biasing member can be a cantilever leaf spring, one end of which being fixed to one of the guide ring and the movable lens frame which supports the spherical follower.
The biasing member can be a leaf spring, wherein the opposite ends of the leaf spring are fixed to one of the guide ring and the movable lens frame which supports the spherical follower.
The one of the guide ring and the movable lens frame which supports the spherical follower can include a holding portion which holds the one end of the cantilever leaf spring.
The one of the guide ring and the movable lens frame which supports the spherical follower can include two holding portions which hold the opposite ends of the leaf spring, respectively.
The biasing member can be a leaf spring portion which is formed integral with the one of the guide ring and the movable lens frame which supports the spherical follower.
The guide groove can be formed on the movable lens frame, and the spherical follower can be provided on the guide ring.
The spherical follower can be made of metal or synthetic resin. The biasing member can be made of metal or synthetic resin.
The guide groove can be formed integral with the one of the guide ring and the movable lens frame which supports the spherical follower if the one of the guide ring and the movable lens frame which supports the spherical follower is molded with synthetic resin.
It is desirable for at least the guide groove to be made of metal.
The present disclosure relates to subject matter contained in Japanese Patent Application No.2001-33302 (filed on Feb. 9, 2001) which is expressly incorporated herein by reference in its entirety.